Pressure relief valve

Abstract

A pressure relief valve is disclosed. The pressure relief valve comprises a valve housing including fluid passageways, a poppet valve disposed within the housing, a piston disposed within the housing, and spring means disposed intermediate the piston and the poppet valve for biasly urging apart the piston and the poppet valve. The poppet valve has a valve seat which, together with a portion of the housing, defines a variable valve area. The piston has a piston area, relatively greater than the variable valve area, for modulating flow through, and pressure drop across, the poppet valve. The pressure relief valve preferably includes an orifice disposed within the housing for selectively controlling flow of hydraulic fluid through the housing passageways to the piston. The housing preferably includes an elongated cage within which the poppet valve is longitudinally slidable.

I claim: 
     
       1. A cartridge pressure relief valve for controlling the flow of fluid between first passageway means and second passageway means in a manifold comprising: valve housing means including a retainer body adapted to be threaded into the manifold and a tubular cage secured within said body and having an inlet and an outlet for respectively communicating with said first passageway means and said second passageway means, tapered annular integral valve seat means disposed within said cage intermediate said inlet and said outlet, a poppet valve having a tapered valve surface slidable within said cage and engageable with said seat means for controlling flow of fluid from said first passageway means to the second passageway means, the taper of said seat means being relatively more acute than the taper of said poppet valve surface thereby defining therebetween a variable valve seat area having a maximum area value and a minimum area value for thereby variably effecting pressure drop of the fluid from a first fluid pressure at said inlet to a relatively lesser fluid pressure at said outlet; spring means engaging said poppet valve within said cage for biasing said poppet valve toward said seat means, said housing means including an internal chamber communicating with said inlet; piston means disposed within said chamber for biasing said spring means toward said poppet valve in response to fluid pressure in said chamber, said piston means having an effective surface area relatively greater in dimension than the maximum area value of said variable valve seat area; and adjustable stop means within said chamber for adjustably limiting movement of the piston means toward said spring means and thereby adjusting the action of the spring means biasing the poppet valve toward said seat means. 
     
     
       2. The pressure relief valve of claim 1 wherein said adjustable stop means comprises an adjusting screw disposed within and axially adjustable relative to said housing means and including a wall separating said chamber from said inlet, said wall including an axial bore slidably receiving said piston means and a second bore communicating with said chamber and said inlet, said piston means including an enlarged head engageable with said wall for limiting movement of said piston means; and a pin slidably disposed in said second bore, said pin and said second bore defining an annular orifice establishing communication between said chamber and said inlet. 
     
     
       3. The pressure relief valve of claim 1 further including orifice means within said housing means intermediate said chamber and said inlet for controlling flow of fluid from the inlet into said chamber and thus the time to fill the chamber with fluid, said orifice means comprising a wall disposed within said housing means separating said chamber from said inlet, said wall including a through bore communicating with said chamber and said inlet; and a pin axially freely slidably disposed in said last mentioned bore, said pin and said last mentioned bore defining an annular orifice. 
     
     
       4. The pressure relief valve of claim 1 wherein said piston surface area is about 110% of said maximum area value of said variable valve seat area. 
     
     
       5. The pressure relief valve of claim 4 wherein said time to fill said chamber ranges from about 100 milliseconds to about 10 seconds. 
     
     
       6. The pressure relief valve of claim 4 wherein said time to fill said chamber is about 1 second when said first and second predetermined fluid pressures are about 700 and about 150 psi respectively. 
     
     
       7. The pressure relief valve of claim 4 wherein said time to fill said chamber is about 5 seconds when said first and second predetermined fluid pressures are about 2000 and 400 psi respectively.